View Full Version : single to three phase

10-25-2005, 08:42 AM
hey guys...

i've been lookin into gettin started on my shop but talked to the power company that supplies the power for my area and they told me i do have three phase to me but they would have to re-run the power poles for the wire to get to my shop...in all...close to $10k or more from what he was saying to put in new poles and the transformers for me...

so long story short, i am lookin into a converter for single into three phase...anyone have any experience or knowledge of these and comments or suggestions as to who i should look into?

thanks in advance

12,000 Doors
10-25-2005, 09:20 AM
I looked into this alot. There are rotary and static phase converters. Rotary is what works with welding machines. Because welders draw so much current they typically need pretty colosal units. Anderson converters wanted to sell me a three hundred pound unit for twelve hundred dollars. Instead I bought a good used two phase welder for $1375. Or you could go buy the book off the internet "How to build a Phase converter", score a big junkyard three phase motor for twenty or thirty bucks and convert it. It's also possible to convert a three phase welder to single phase by bypassing one of the three transformers ( the third transformer would draw too much current on single phase) and wiring the other two as if they were one, making sure you don't have a three phase fan motor in it. Still anouther way to deal with the problem would be to go buy a three phase generator/welder for three thousand dollars (Miller Bobcat three phase). Now you know why those used three phase welders typically are so cheap.

10-25-2005, 10:42 AM
No- no- no,the reason shops bring-in 3 phase is the savings in energy use and effiency. Going the root of generators will suck you dry in fuel. Most poeple don't know in new power welders that are transformerless and switch to any Phase.
Just as I bought a $100 unit plasma 3 phase unit-waste of time and money-junk.
Here is a good cheap 3Phase generator---get a ( Frieghtliner) tractor rig alternator-take the diodes and sensor unit out- now you have-60-100 amp-3 phase unit generator to run any unit--just run it off the rig.

10-25-2005, 10:48 AM
You will learn a lot if you do an eBay search of three phase converters, books, instruction, etc.

10-25-2005, 01:00 PM
I have a couple of 3-phase motor I am going to use to build a simple small phase converter, just as a project to learn with (2hp and 5hp). For a welder, you will need about a 20-40 hp phase converter, depending on the welding amps. These things are big, big, big.

Geo1671 is right. The real benefits of three phase is power efficency and also the ability to use really simple motors that can be HUGE. You can also run higher voltages (440-480 or even 560 or more), which reduces the expence at the breaker box and for wiring (at least, that's the way I understand it). Single phase has limitations on how large the motors can be, but I still have a bunch to learn about this issue and am not an expert by any stretch of the imagination.

In my area, the price of single and three phase power is the same per kwh, but the setup is where they really ding you. I talked with a guy a while back who worked with a local EMC. He said that three phase just requires more in infrastructure and they have to recoup it in the installation (unregulated charges). Ideally, you would want to find a place that already has 3-phase, so you dont have the installation costs, but there you will probably be looking at a higher price for the shop space.

10-25-2005, 02:48 PM
just doin a search for converters, i came across a bunch of places that sell 1-to-3 phase converters big enough to power a deltaweld or invision welder for about $1200-1900...thats only goin by the info on the sites but they say the size needed is dictated by input power for the welder x 50%...i was lookin at a CP-302 miller which requires 33 amps input...33 x 50% = 49.5 amps roughly...and a converter that's gonna run me about $1500 average is hella cheaper than $10k or so i was quoted by my EMC...

am i reading that right?...here's the info i got from one company...
"Booster™ three phase conversion with welders...Boosters™ are designed to run induction motors most efficiently. Welders can also be operated but the converter size should be chosen to be larger than the welder input power by 50%. If no power rating is shown then multiply the welding current by 50 for E series converters or by 30 for D series converters. The result will be the converter power rating in Watts for 100 % duty factor, often misnamed duty cycle."

10-25-2005, 03:04 PM
Sounds about in the ballpark of what I have seen on other converter sites. It is cheaper, but it is not a perfect solution. There are some issues with starting converters that large. I have read some postings of folks browning out their neighborhood when starting a 15hp converter. There is also the issue of who is responsible for the equipment. If the EMC installs a line and stuff and run you the power, they will be responsible for equipment failure. With a converter, you are on your own, in that respect. The converters work, however. There are several machine shop forums and woodworking forums that have dedicated threads to phase converters, so, there is knowledge out there and also many long-lived converters working like tops. Saving money on used 3-phase equipment is a big plus. Gaining the simplicity and efficiency of the 3p motors is also a plus. $10k is NOT an attractive price at all. $1500 is more attractive. If the price is right for you, I'd say go for it. You could use it until you get things going, and if things work out great, you can spend the $10k and add 10% on every invoice until it's paid for. If you have other income, you can use it as a business expense and save up to 1/3 of the price in taxes (depending on your marginal bracket). You could also get the EMC solution and charge admission for all us 3-phase wantabees.;)

10-25-2005, 03:28 PM
yeah i see where you're coming from...i am gonna give the guys at the EMC one more try to make absolutely sure we are both in the same ballpark and that i know i'm not making a huge (and costly) mistake here...then, if it is true about the cost being that high, i will look further into the converters.

11-03-2005, 08:28 AM
how big of a welder do you need? unless you really need a lot of big welders going at the same time three phase would not be cost effective, nor would a generator, or phase converter. To run a 20 hp rotoray converter would cost you a lot of bucks. NOt to mention that it is very hard to get all three phases balanced with a motor and caps to get true three phase power. I don't know if it would have a negative effect on the electronics or not. If you were a bussiness with three of four guys welding, then I would consider it. Remember to run a converter you have efficiency loss, probably at least 20% of your electric is wasted converting power.

I have several motors that I have converted for lathes and radial arm saw, and things like that. I use them because they came with or I had gotten really cheap three phase motors.

the advantage of 3 phase is smaller wires, service, and higher torque for motors, and no starting components. IMHO you would be wasting all of the investment in three phase. If you need more power put in a 400 amp service.

11-03-2005, 10:39 AM
I think you are right on all your technical points about converters, but I am not sure ralin93 is necessarily after maximum technical efficiency, but more after a bit of risk avoidance in a new and uncertian business venture. Like many starting businesses, he is probably thinking about minimizing fixed, non-recoverable costs.

Most of the old big welders have little or no electronics (printed circuits), but based on my understanding you are right on the mark about the converter not providing perfect 3p power and generally not being the best route for welding applications. These things are used to run machinery like you mention, with motors. But, if you can pick up a few of these machines (that you actually need, that is) that would cost you $1000+ in 1p for $100 in 3p, a converter starts to look attractive, given some of the alternative costs of true 3p service. But to repeat, welders are not where you generally save money, though.

I think the point brought out in the thread is that if railin93 intends to go the three phase route, he might start with used cheap 3p machinery and a converter until business picks up, and then pop for the full service (or move the business to a facility with the service) and sell the converter. That isnt unreasonable, if he can find some real deals on 3p tools. It might be well worth the investment...maybe.

One risk is that if he starts out with single phase machinery and finds they do not adequately meet the needs of a growing buisness, he is faced at some point with both re-tooling and comming up with the bucks for the 3p anyway, but if business is booming, maybe a big loan is in order, but that also depends on lots of other stuff. Maybe the worst case would be if he bought the 3p service and the business didnt fly. As far as I know, an emc will not buy back the $10,000 worth of equip and installation and he might simply be out the full price of the setup...so, the decision is really not as clear cut as it might first appear.

Probably everyone on this site wishes he had three phase power, and converters are not a perfect solution...especially not for welders. If they were, we'd all have one. But, they can provide a middle ground for some equipment in over an uncertian business period at a relatively low intro fee. Self-employment and business ownership are not for the faint of heart, but even the big dogs make decision trees and think about cost recovery in case of failure. I want to make it clear that I am not disagreeing with you on any of your points, because you are right. I just think some of the decision process in this case might involve more than technical issues.

11-04-2005, 07:59 AM
yes I see what you mean, I wasn't sure exactly what he was looking for. and I agree with you. LIke I said I have three phase equipment, and build three phase converters (rotary) to run them, and all the parts I got for free, as most people can;t use three phase motors. If you are going commercial it makes it more complicated. thanks for the clarification.